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How many Americans die from smoking without even lighting up a
cigarette? More than 42,000 people a year, including 900 infants,
according to a new, thorough analysis of secondhand smoke deaths
by researchers at the University of California, San Francisco.

Altogether, that's 600,000 years of potential life lost — an
average of 14.2 years for each nonsmoker who has died prematurely
as a result of someone else's smoking — amounting to $6.6 billion
in lost productivity.

The early
deaths disproportionately affect African-Americans,
especially black infants. And the researchers said they are
likely underestimating the true impact. Their results are
detailed this month in the American Journal of Public Health.

Even so, according to a Gallup poll conducted July 9-12, many
smokers and nonsmokers are unaware of secondhand smoke danger,
with just 28 percent of smokers saying secondhand smoke is very
harmful to adults, compared with 63 percent of nonsmokers. Nearly
one in four smokers said secondhand smoke is not too harmful or
not harmful at all.

Gets in your blood

The U.S. Centers for Disease Control and Prevention (CDC) has
estimated that secondhand smoke causes about 49,000 deaths
annually. The data supporting this, however, rely primarily on
self-reporting to gauge
secondhand smoke exposure, which many researchers consider
unreliable.

Furthermore, given the poor air quality in most large American
cities, calculating the number of
deaths among nonsmokers due to secondhand smoke — as opposed
to diesel fumes and coal burning, for example — has been
difficult for researchers.

The UCSF researchers took a fresh approach by basing their
numbers on a chemical called cotinine in the blood, which is a
byproduct of smoking proportional to the amount of exposure to
tobacco smoke. Most of us have cotinine in our blood; but those
who are exposed to lots of secondhand smoke at home or, for
example, at a bar, will have higher levels. [ Never Too
Late: 5 Habits You Should Still Quit ]

This is the first estimate of secondhand smoking deaths and
economic impact based on serum cotinine, said the study's lead
author, Wendy Max, professor of health economics at the UCSF
School of Nursing.

An underestimate

The new study shows that the statistics on fatalities resulting
from
ischemic heart disease are 25 percent lower than previously
reported (34,000 deaths compared with 46,000), but nearly twice
as high for lung cancer deaths (7,333 deaths compared with
3,400).

Nevertheless, this is likely an underestimate, Max told
LiveScience. She said the number of deaths her team calculated is
a statistical estimate, not an identification of particular
individuals.

"It is true that
smoking is banned in many public places and workplaces," Max
said. "However, our use of the biomarker indicates that people
are still being exposed more than we realized. Much of this may
be at home, but not all. Studies show that even small amounts of
secondhand smoke exposure may have a negative impact on health,
particularly for people who are vulnerable for various reasons."

The vulnerable include newborns, either exposed in the womb or
after birth, and adults with existing heart and lung problems.

The largest toll is on African-Americans. Blacks accounted for 13
percent of all deaths, but up to 36 percent of infant deaths.
Black adults had significantly greater exposure rates than did
whites in all age groups.

"This burden results in communities of color suffering relatively
greater losses," both in health and economic potential to their
communities and the nation, the researchers wrote.

The UCSF researchers relied on date from several sources,
including the National Health and Nutrition Examination Survey,
the National Health Interview Survey, and the Multiple Cause of
Death data file, which contains records of 2.4 million deaths.

Christopher Wanjek is the author of a new novel, " Hey,
Einstein! ", a comical nature-versus-nurture tale about
raising clones of Albert Einstein in less-than-ideal settings.
His column, Bad
Medicine, appears regularly on LiveScience